Apical cytoplasm

About: Apical cytoplasm is a research topic. Over the lifetime, 1080 publications have been published within this topic receiving 36131 citations.

Ultrastructure of the mushroom body: digestion during metamorphosis of Utterbackia imbecillis (Bivalvia: Unionidae)

Abstract: Larvae of the freshwater mussel Utterbackia imbecillis metamorphose to juveniles either during their attachment to a host fish, or in vitro in a culture medium. This transformation includes degeneration of larval structures and development of the juvenile morphology. Early in metamorphosis the cells comprising the larval mantle enlarge and project into the mantle cavity, forming a structure referred to as the mushroom body. Its cells, which are ultrastruc- turally very similar to digestive cells of adult bivalves, are involved in pinocytosis or phago- cytosis of the larval adductor muscle and of tissue from the host fish that is enclosed between the larval shells. Ingested material is passed from pinosomes to heterophagosomes which in turn fuse with heterolysosomes, where final degradation of ingested material occurs. Acid phos- phatase activity was detected in heterophagosomes and heterolysosomes of all animals exam- ined. In larvae that metamorphosed in vitro, the apical cytoplasm of the cells of the mushroom body, and the extracellular spaces among them, also exhibited acid phosphatase activity. Larvae reared on a host fish accumulated substantial deposits of lipids and glycogen within larval mantle cells during metamorphosis, whereas larvae reared in vitro did not. The larval mantle cells which constitute the mushroom body appear to be the primary sites of intracellular di- gestion of the larval adductor muscle and host tissue during metamorphosis.

M cells in the rabbit palatine tonsil : the distribution, spatial arrangement and membrane subdomains as defined by confocal lectin histochemistry

Abstract: The crypt epithelium of the palatine tonsil contains M cells that play an important role in the uptake of luminal antigens to initiate immune responses. To study the close interaction of M cells, squamous epithelial cells and lymphocytes we used confocal laser scanning microscopy and the lectin from Ulex europaeus (UEA-I), which selectively labels rabbit tonsillar M cells. Confocal serial sections and synthetic section planes showed that the M cells comprise up to 35% of the epithelial cells in the tonsil crypt and completely engulf clusters of two to eight lymphocytes with their apical cytoplasm. These lymphocytes lie in a pocket of the M cell’s basolateral membrane that invaginates from one of the lateral aspects and forms a tunnel-like opening. Therefore, the tonsillar M cells closely resemble the M cells of the small and large intestines in their spatial structure, and likewise maintain an intraepithelial compartment for the interaction of lymphocytes, macrophages and antigens. The UEA-I bound intensely to the apical membrane of the M cells and to transcytotic vesicles in the apical cytoplasm. The pocket membrane bound the UEA-I more avidly than the remaining basolateral membrane, suggesting that the basolateral membrane of M cells is subdivided into membrane domains with different compositions of glycoconjugates.

Changes in the apical microfilaments of rat uterine epithelial cells in response to estradiol and progesterone.

Abstract: This study investigates the interaction of hormones and the cytoskeleton within the apical cytoplasm of uterine epithelial cells of the rat. The effects of the hormones estradiol-17 beta and progesterone on the microfilament configuration were studied using myosin subfragment 1 (S1) decoration of actin microfilaments (MF) and transmission electron microscopy. In control ovariectomized animals, a sparse MF distribution was found in the apical cytoplasm underlying short microvilli with S1-decorated core MF. Hormone treatment experiments consisted of injecting ovariectomized rats with either progesterone or estradiol-17 beta. For the study of the MF configuration accompanying an apical surface primed for blastocyst receptivity, progesterone treatment was immediately followed by a single dose of estradiol-17 beta. The long, regular microvilli associated with estradiol only treatment contained bundled, decorated MF with tightly bundled rootlets. Progesterone alone produced numerous short microvilli with decorated core bundle MF and pronounced rootlets that frequently appeared splayed. The irregular microvilli and luminal surface of the uterine epithelial cells associated with the receptivity hormone sequence contained variable MF configurations, including MF bundles, networks, and areas with a "felted" appearance. The results show that the various hormone regimes produce characteristically different MF configurations and that this component of the cytoskeleton appears to be under the control of a delicate hormone balance within these uterine cells. The responses of uterine MF to specific regimes of steroid hormones used in this study are not only important for the understanding of the mechanisms at work during early pregnancy, but also contribute to the body of knowledge concerning the ways in which hormones in general effect the cytoskeleton of target cells.

Variations in immunocytochemical localization of cathepsin B and thyroxine in follicular cells of the rat thyroid gland and plasma TSH concentrations over 24 hours

Abstract: Immunocytochemical localization of cathepsin B and thyroxine (T4) in follicular cells of the rat thyroid gland and plasma concentrations of thyroid stimulating hormone (TSH) were examined at six evenly spaced times over 24 h. By light- and electron microscopy, immunodeposits for cathepsin B were localized in cytoplasmic granules of various sizes, whereas those for T4 were detected mainly in larger granules of the cells and in the colloid lumen. The size and location of cytoplasmic granules showing immunoreactivity for cathepsin B and T4 in the cells varied over 24 h, corresponding to a change in plasma TSH concentrations. These immunopositive large granules appeared in the apical cytoplasm at 12.00 h, when the level of TSH was highest. At 20.00 h when the level of TSH was lowest, T4-positive granules almost disappeared, and cathepsin B-positive small granules were abundantly seen in the basal region. From 00.00 h to 08.00 h, these positive granules changed in the same manner as those seen from 12.00 h to 20.00 h, associated with an increase in plasma TSH levels. These results suggest that newly formed colloid droplets migrate from the apical to the basal regions. Cathepsin B may play a role not only in the degradation of thyroglobulin but in the maturation of thyroid hormones during the migration of the granules.